Hi Eli,
First, you are wise to ask about whether or not you need to finish the rest of the body before face rigging. The answer is no. There are a number of ways to hook your face rig into a full character rig without re-doing any blendshapes etc. Such as using an explicit wrap deformer for example.
The topolopgy is very important. Faces will NOT deform in any half decent way if they have badly thought-out topology or are too low res. In your case, the general shape and form of this character is rather poor....I don't mean that as insult, rather to push you into spending more time on it before rigging it. you NEED to work from reference if you want a character's head, particularly a human (that is subject to our perception) to look good or real....neither of which are words describing this model. Put some image planes in and go from photographs. You need to always be asking yourself, with regards to any task in CG...."does it look like the picture in my head?" If the answer is no, then ask why not, and whats wrong, and tackle those things one by one. Good CG is all about method, and finesse. No CG is ever finished, only abandoned. In the case of this model, it is not even close to being ready for rigging. I'm not sayign its bad or rubbish or anything. I'm sayign its not ready yet. Work on it a lot more. In terms of topology, it seems to me as though you have more or less the right idea....loops around contours, very good. The shape needs work as I said, but basically the right idea. What your lacking topology-wise, is continutity and resolution. I can see a lot of dirty little tri's in there. I also see very differing face/edge sizes in all areas of this face. For example.....the lips do not have enough density to form actual words or facial expressions with...yet they are twice as dense as the very sparce areas around the mouth...like the chin....just 1 vertex above and below the chin before your into the mouth or neck. What do you think will happen to those areas when the verticies move around? How do you expect to hold shape and volume without verticies there to form the shapes? And the neck....how is that going to bend or twist or maintain any volume or anatomical detail? Same goes for the forehead and the back of the head when the head tilts... My advice, although density of verticeis does need to alter through different areas of a face/head, it should vary THAT much and should be kept as even and as tidy as possible, if you want it to deform nicely. Remove the tri's, and watch where your putting your kites....like the ones that are interfeering with your eyelids. That won't go well at all. Best place to extend loops to for position of the kites is often above the eyebrows into the forehead, or better still, all the way over to the back of the scalp.
As for hair....no, its an entirely different subject all of its own, whether is just simple skinned.textured geometry, or dynamic hair simulation. LEave that until the rest of the character is complete in my opinion.
Hope that helps.